1. Field of the Invention
The present invention relates to central tire inflation systems (CTIS), also known as on-board inflation systems and tire traction systems, wherein the inflation pressure of one or more vehicle tires may be controlled from a remote location (usually the vehicle cab) with the vehicle at rest and/or in motion and utilizing an on-board source of pressurized fluid (usually compressed air from the vehicle air brake compressor and/or a compressed air reservoir). In particular, the present invention relates to an adaptive control system and method for an on-board central tire inflation system which minimizes the time required to deflate a tire to a selected pressure and reduces the difference between tire pressure after deflation.
2. Description of the Prior Art
Central tire inflation systems, also known as tire traction systems, are well known in the prior art as may be seen by reference to U.S. Pat. Nos. 2,634,782; 2,976,906; 2,989,999; 3,099,309; 3,102,573; 3,276,502; 3,276,503; 4,313,483; 4,418,737; 4,421,151; 4,333,491; 4,456,038; 4,434,833; 4,640,331 and 4,678,017, the disclosures of all of which are hereby incorporated by reference. CTIS allow the operator to remotely manually and/or automatically vary and/or maintain the inflation pressure of one or more of the vehicle tires from the vehicle (usually a truck) air system, usually while the vehicle is in motion as well as when the vehicle is at rest.
It is well known that the traction of vehicles on relatively soft terrain (i.e. on mud, sand or snow) may be greatly improved by decreasing the inflation pressure within the tires. By decreasing the inflation pressure, the tire supporting surface (usually called the "footprint") will increase thereby enlarging the contact area between the tires and the terrain. Additionally, it is often desirable to decrease the tire pressure from the over-the-road or highway inflation pressure to increase riding comfort on rough roads. On the other hand, higher tire pressures decrease rolling resistance and tire carcass temperatures on smooth hard roads thereby increasing economy and safety. Accordingly, in cross country vehicles it is desirable to change the inflation pressure in the pneumatic tires to fit the terrain and is also desirable that a system be provided for changing the inflation pressure of the tires from an on-board source, while the vehicle is at motion or at rest and that the system be controlled from the vehicles operating cab.
In a particular type of CTIS, as illustrated and described in above-mentioned U.S. Pat. No. 4,640,331, a plurality of wheel ends (each comprising one or more tires) are each fluidly connected by a separate branch conduit to common central conduit which may be connected to a source of pressurized air for inflating the tires, to a source of regulated pressurized air for deflating the tires and/or, to atmosphere for venting the conduits and relieving pressure across the rotating seals. The common conduit may also be pressurized by means of one or more quick release valves or the like to the average pressure of each or all of the various branch conduits. A single pressure transducer is provided in fluid communication with the common central conduit, remote from the wheel ends, for sensing a value indicative of the pressure or average pressure in the inflatable tires.
Typically, periodically (about every fifteen minutes) the CTIS would automatically check tire pressures to determine if correction is necessary.
While the on-board CTIS described above is highly advantageous as pressure venting is remote from the wheel ends and a single pressure transducer, located in a relatively well protected location remote from the wheel ends and/or the vehicle under carriage, can be utilized to sense tire inflation of the vehicle tires or groups of tires, the CTIS was not totally satisfactory as adaptive control methods were not provided to minimize the time required to deflate the tires to a selected pressure. Additionally, if a plurality of groups of tires, each group connected to the common conduit by a separate quick release valve, were being deflated, the prior art systems tended to deflate all of the tires only until the lowest pressurized group of tires was deflated to the selected inflation pressure.